WW-P 9-12 Schools

Grades 9-12

Homologous structures are structures with the same origin, but now have different functions.  This occurs through divergent evolution.  For example, a human arm, a bat's wing, a seal's flipper, and a whale's front fins are all composed of almost the same bones, however their functions have changed through evolution.

This is a picture of a slug, which, like the llama, is in the kingdom animalia but in a different phylum.  The slug is in the phylum mollusca.  All molluscs are unsegmented and are bilaterally symmetrical.  Some examples of animals in the mollusc phylum are cuttlefish, squid, octopus, snails, and slugs. 

This is a picture of a llama, which is an example of an animal in the phylum chordata.  Most Chordata's are classified by their spinal cord which makes them vertebrates. Other characteristics include a complete digestive system, endoskeleton made of bone or cartiallage, and a closed circulatory system.  Humans are also included in this phylum.

The definition of a population, as I said in an earlier post,  is all the organisms that belong to the same species and live in the same geographical area.  However, in this post I'm going to talk about how that geographical area is defined.  The area is defined as where interbreeding is possible between a pair, and is more likely than crossbreeding with individuals from outside the area.  Using this fishtank as an example, breeding is likely inside the fishtank, but it would be pretty difficult for fish inside the tank to breed with fish from outside the tank.

Homeostasis means to have a constant state of properties such as temperature, pH, and others.  This is a picture of a bird which is an endotherm, which also means it is a regulator.  Regulators use internal mechanisms to control internal change when external conditions are fluctuating.  For example, the bird is a regulator when it comes to temperature.  When the external temperature changes, the bird's internal temperature stays relatively the same because of the internal mechanisms.

Another example of homeostasis(look at post below for definition) is a freshwater fish.  Freshwater fishes, also regulators, can maintain stable internal concentrations of solutes in its blood, even though the concentration differs from the solute concentration of the external water it lives in.

The term long-day plant is pretty self explanatory.  It is a plant which needs long days and short nights for flowering to occur.  In the northern hemisphere, these plants flower in the late spring or early summer when the days are getting longer.  This is a picture of lettuce which is an example of a long-day plant along with peas, barley, and some types of wheat.

A population is a group of individuals of the same species living in a particular area.  Here is just a small portion of a population of geese in a grass field.  

Ethylene is a plant hormone which regulates opening of flowers, shedding of leaves, and ripening of fruit.  These bananas ripened from green to yellow because of this hormone.  Ethylene can also be used for commercial purposes to ripen fruits faster.